HU200568B - Method and apparatus for tghtening respectively releasing - Google Patents

Description

The present invention relates to a method for tightening or loosening screw connections έε. Applications are mainly mechanical and assembly industries, where screw joints have to carry high forces, such as precision engineering, where it is often necessary to provide a large series of screw joints with high precision and a predetermined amount of pre-tension.

A variety of devices are known for tightening or loosening screw joints, which differ in the direction of movement used, the mode of loading, and the handling. In terms of their function, known devices fall into three groups: power screwdriver, impact screwdriver, and vibrator screwdriver. The operation of a screwdriver is essentially the same as a manual screwdriver, in which a force is applied to a wrench or the like by means of a lever, but here human power is replaced by mechanical force, for example electric, pneumatic or hydraulic. Such solutions are described, for example, in DE PS 2 529 818 and DD 62 789. These differ primarily in the design of the elements used to transmit power to the screws to be rotated. In the first solution a strap is used for this purpose, while in the second solution a combination of a locking ring and a latch is suggested.

Impact screwdrivers measure fast impacts on the bolt section to be tightened or loosened during screwing. Thus, the impulse energy of the impact-rotating assembly causes the nut to move in the opposite direction. Such high-frequency impact screwdrivers are generally AC powered and have a beat frequency of up to 500 Hz.

All drive modes mentioned above are also used for impact screwdrivers. Often, however, a primary electric drive is used which then exerts its impact through an intervening hydraulic or pneumatic structure. Such a solution is described in DE OS 3 231 902.

During operation of the impact driver, unpleasant vibrations and noises occur, so manual operation of them for an extended period of time will put too much physical strain on the operator. Compared to power screwdrivers, these impact screwdrivers have a much higher maximum torque and are therefore manufactured as handheld for relatively low torques.

In the above solution, there is no clear limit on the torque, since the quality of the contact surfaces, the quality of the friction materials and the friction coefficients that are reduced by vibration, are increasingly influencing the torque required for rotational motion in the area of maximum load. The high mechanical stress of the devices places very high demands on the abrasion resistance of the individual components.

As is known, in some applications it is important that all bolted joints are tightened evenly, which in the case of automatic equipment requires precise adjustment of the torque limit of each device. For example, this is not available with a sliding clutch.

DE OS 2 835 382 discloses a circuit arrangement for torque tripping of an electric motor driven speed controlled impact screwdriver. At these load resistors, a cute voltage is applied to the motor under load, and the current is generated by a summing device in the integrator during the impact screwing operation, the sum of which is decisive for the applied impact energy. A voltage proportional to this power is then compared to the rated value in a comparator and, if any, is disconnected from the motor.

Although this switching arrangement is capable of interrupting the screwing process as a function of the last stroke when the maximum torque is exceeded, this solution has negative effects, e.g. equalization or elimination of frictional forces dependent on surface, material, and tensile strength cannot be satisfactorily resolved. Higher accuracy requires frequent authentication, which should cover all possible changes, such as. also if the bearing surface of the material changes.

A third group of known devices is a vibrating screwdriver used in the range of 4 to 60 kHz. Such a vibrating screwdriver is described in DE OS 2 354 346. According to this, during the process of screwdriving, the tool, the screw or one of the components to be connected are subjected to vibration at which they operate at a preselected frequency.

Thus, the frictional resistance and consequently the required torque can be significantly reduced, but the disadvantage is that the torque as an indirect measure can no longer be applied to the tension of the screw spindle. No information can be learned from the above document on how to obtain tensile stress information, which is a basic piece of data for most technical bolting operations. It is perhaps these problems that have caused such devices to spread only sporadically in practice.

HU 200568 Β

SUMMARY OF THE INVENTION The object of the present invention is to overcome the above shortcomings, i.e. to provide a solution for tightening or soldering screw joints which can be applied with the same high accuracy for different sizes of screw joints and screws, and in particular able to tighten many screw joints simultaneously. Furthermore, the inventive solution must be reusable, simple and safe to handle and relatively inexpensive to produce in series.

The object of the present invention is therefore to provide a solution that provides energy-saving, precise control and overloading of all materials, and the device is sufficiently compact and robust to adapt to various screw connections and screwdrivers.

The object of the present invention has been solved by a method of excitation of the screw spindle by longitudinal vibrations, measuring the self-frequency, adjusting the excitation frequency during screwing according to the variable self-frequency so that the screw spindle remains in resonance and in the stretching or contractioning phase, so as to relieve the vibrating spindle from the tensioning or compressive stresses.

Preferably, the self-frequency is used as benchmark data for the use of the screw spindle 35 and compared with the spindle boundary voltage, at which point the excitation is interrupted and the screw tightening operation is completed. 40

Preferably, the piezo-electric motor for screwing is controlled so that the excitation frequency is equal to the spindle frequency of the screw spindle.

For the simultaneous tightening of at least two screw joints and 45 equal steps, the process of the present invention may be carried out in a stepwise manner, first by tightening the screw to the first nominal value corresponding to the maximum prestressing force, and after this first nominal value is reached for each screw joint. In this case, proceed with further stepped nominal values until the last nominal value is reached. 55

The excitation energy can be adapted to the screw process by increasing the excitation energy continuously or intermittently as soon as the self-frequency of the screw spindle remains constant during the stagnant screw process and continues up to the nominal value.

The process according to the invention can be carried out by means of a device which preferably has a motor drive unit and a unit for directly or indirectly measuring the need for the screw spindle. The essence of the device according to the invention is that the screw spindle is associated with a vibration transducer detector unit which is designed and supported by a vibration transducer, and that piezo electric element is connected to an alternating current generator, which is connected to a differential generator. The difference generator is also connected to a vibration sensor and feedback to the alternator.

An embodiment in which the vibration transducer detection unit is configured as a ring-shaped piezoelectric element is desirable.

This piezo-electric element may be disposed between the screw head or nut and the flange, and is provided with a power supply and signal transmission cable. Alternatively, the piezoelectric element is located between the vibration transfer unit and the tubular key housing.

The invention will be described in more detail with reference to the accompanying drawings, in which some exemplary embodiments of the present invention are illustrated. In the drawing:

Figure 1 is a longitudinal sectional view of a screw connection with a first exemplary embodiment of the apparatus of the invention;

Figure 2 is another longitudinal section of another embodiment of the solution of Figure 1;

Figure 3 is a schematic diagram of a first exemplary embodiment of the apparatus of the invention;

Figure 4 is a schematic diagram of a second exemplary embodiment of the apparatus of the invention;

Figure 5 is a schematic diagram of a third exemplary embodiment of the apparatus of the invention.

The device according to the invention is well adapted to a variety of application requirements. This applies equally to the magnitude of the force to be transferred as it applies to high-tech processes such as robotics. Due to the robustness, relatively small space requirements and reliability of the device according to the invention, it is very economical, easy and simple to operate, and can be operated both by motor and by hand.

Figure 1 illustrates a flanged pipe joint having a piezo-electric element 2 between the nut 4 and the flange 6 and provided with a transverse vibrating device which acts as a compact vibration transducer unit. The piezo-electric element 2 is thus both a vibration transmitter and a res-35

EN 200568 Β also functions as a motion detector. To this end, it is provided with a power supply and signal transmission wire 3, which is connected to a control circuit not shown here. If the piezo-electric element 2 is to function only as a vibration transducer, then separate vibration sensors 12 and 13 can be provided, which receive the vibrations to be measured and transmit the measurement signals to the control circuit. This arrangement can be described as employing a spatially spaced vibration transducer unit. It is not necessary to use piezoelectric vibration sensors 12 or 13 here, for example, a strain gauge sticker affixed to a screw spindle 1 may be used. As shown in Figure 1, the rotation of the nut 4 and thus the tightening or loosening of the screw connection is performed by a motor drive, which in this case is designed as a piezo-mechanical rotary drive. The motor housing is substantially identical to the key housing 9, the lower part of which is provided with an internal polygonal opening for receiving the nut 4. Preferably, this lower part can be replaced for different size nuts according to different wrench sizes.

A rotary vibration generator 8 is provided between the tubular key housing 9 and the powder core 10. The powder core 10 is provided as an axial projection with a coupling head 11 which passes through the wrench housing 9 and serves to counteract the manual tightening or loosening of the screw connection and to increase the powder core as required.

Figure 2 shows the arrangement of a more compact vibration transducer assembly. Here, the flanges 17 and 18 lie on top of each other so that the other screw end, not shown separately, is not accessible, i.e., it is not possible to arrange a separate vibration sensor thereon. Consequently, a compact vibration transducer sensor unit is used, which may be arranged between the nut 4 and the flange 6 (as shown in FIG. 1) or, as shown in FIG. 2, between the end face of the tubular housing 9 and the vibration transducer 14. In the latter version, the vibration transmitter is essentially mounted on 15 screw heads. Again, the piezo-electric element 19 is a transverse oscillator, which can operate as both a vibration transmitter and a vibration sensor. The coupling head 11 serves the aforementioned function and may also be used to connect a separate drive. Of course, the construction layout shown in Fig. 1 is also applicable here and is also required for automated processes.

Above, some important embodiments of the vibration transducer and vibration detector unit forming part of the apparatus according to the invention have been described, these structural parts being directly or indirectly connected to the screw connection and forming a structural unit. In the automatic screwing process, these assemblies can be arranged in a common flexible frame and connected to the rest of the equipment via cable.

Figure 3 illustrates the simplest conceptual circuit diagram of an apparatus according to the invention in which the compact vibration transducer unit is dimensioned to the minimum requirements. Here, the piezo-electric element 19 is connected via a power supply and signal transmission line 3 to an alternator 21 of variable frequency and power, which causes the piezo-electric element 19 to vibrate. In order to solve the screwing operation of screws of various sizes with a single generator 21, it must have a wide frequency range, which in this case is chosen from 50 Hz to 5000 MHz. The same applies to performance, since the higher the swinging mass, the greater the preload of the screw connection and thus its self-frequency.

From a measuring point of view, the connection between the AC generator 21 and the piezo-electric element 19 is configured as a vibration detector on the one hand and as a difference generating unit 22 via a signal line 25, on the other. In the case of compact vibration transducer units, this is possible through a single signal line 25, since the power supply and signal transmission lines 3 can be conducted in a single cable. Measurement of the tidal frequency and the excitation frequency via said 25 signal lines may be performed in the measuring and excitation phases with a time shift. By using a separate vibration sensor, additional connection to the difference generator 22 must be provided. An additional signal line 26 may be used as feedback from the differential generator 22 to the alternator 21 to influence the excitation frequency and excitation power. In the exemplary embodiment of Figure 3, there is no such electrical influence between the drive 20 and the control lever. The drive can be motorized or even manual.

Figure 4 is a schematic diagram of a device having a plurality of screw locations formed by multiplying the apparatus of Figure 3. We provided 23 units with a common setpoint value. Particularly preferred piezo-mechanical drives 24 are connected by a power line 28 to AC generators 21 which are of the same frequency and supply the piezo-electric elements 19. Thus, according to our experimental experience, very high energy efficiency can be achieved.

Figure 5 is a further exemplary circuit diagram of an apparatus having multiple screw locations. In this case, the assemblies of drives 24 and piezo-electric 19 are connected to a single control circuit, which is thus common

EN 200568 Β is supplied with an alternator 21 and a differential unit 22. The connection is provided by a power and signal line 29, which is interrupted by a program selector switch 30. The program selector switch 30 establishes the appropriate connections in a predetermined order. When using a cascaded nominal value - which is applied to the differential unit 22 via signal line 27 from the unit 23 giving the specified value, a screwdriver that is sufficiently suitable for the various applications can be achieved, even though only one device is always in operation.

The mode of operation of the apparatus for carrying out the process of the invention is described below in more detail:

The process of the present invention utilizes the elastic properties of rigid bodies, namely that they can be oscillated when properly excited, with varying geometric dimensions within certain limits. In order to facilitate tightening or loosening of the screw joints, it is desirable to relieve the screw 1, threaded tube or the like from the tensile or compressive stresses during the screwing operation. This is achieved simply by excitation of the screw spindle 1 with longitudinal oscillations and bringing it into resonance. For this purpose, a vibration transmitter, preferably a piezoelectric element 2 or 19, is used, the excitation frequency of which is controlled according to the self-frequency, which in turn also changes due to the varying voltage during the screwing operation. To achieve proper elongation or contraction of the screw spindle, the excitation energy is increased until the nut 4 or the screw head is easily turned. The power output required to bring the screw joint into a resonating oscillating motion is only a fraction of the value used in conventional equipment. The present invention takes advantage of the discovery that short-term resizing of workpieces in the elastic region of materials is significantly more beneficial by producing resonance. Depending on the magnitude of the excitation energy to be transmitted, the screw spindle 1 is relieved to a greater or lesser degree in the resonance frequency section.

Thereby, a relatively easy slip is created between the contacting threads and the contacting surfaces of the nut 4 and the piezo-electric elements 2 and 19 during screwing. Furthermore, the adhesive friction to be overcome no longer plays a decisive role and can be completely eliminated if the excitation is sufficiently strong.

The self-frequency serves as a decisive measure of the voltage of the screw 1 and increases progressively with the increase in voltage. Therefore, even in the case of precision screw connections, very well coordinated voltage values can be achieved using the present invention. By validating the screw spindle 1, the relationship between the voltage value and the self-frequency is given. By comparing the variable self-frequency during the screwing operation, the screwing operation is limited by comparing the self-frequency with the nominal value determined from the calibration curve. As soon as the power supply and signal transmission line 3 are disconnected from the vibration transmitter and thus the vibration state of the screw spindle 1, the connection of the nut 4 is immediately biased to the screw spindle and can only be subsequently turned with great force. It is also advantageous to use the present invention because undesirable torsional stress does not occur even at stresses greater than those of the slender screw spindles.

There are two ways to protect the screw spindle 1 against overloading, for example, in the event of a failure of the unit having the desired value 23. On the one hand, the self-frequency of the screw 1 can be measured successively and compared, they are greatly reduced when the maximum tensile stress is exceeded, or on the other hand, by comparing the self-frequency with the excitation frequency of the generator 21, which This will trigger a sign when the maximum load is exceeded. In both cases, the tightening process stops immediately and the overload protector, as appropriate, gives a signal. In the latter case, however, it may be necessary to have a certain relative overrun of the excitation frequency if the excitation frequency is allowed to exceed the self-frequency within certain limits.

A particularly advantageous drive mode is provided by the piezo-mechanical motor, which can be controlled to the same frequency as the self-frequency of the excitation or screw spindle. This ensures that the drive 24 only consumes energy when the screw spindle 1 is in the pulling phase and thus work can be performed by turning the nut 4.

In the case where several bolted joints are to be tightened simultaneously and evenly, it is advisable to use a sliding nominal value, that is, work with a controlled nominal value following the target value. In this case, one of the screwdrivers for the screw connections performs the function of a control unit whose frequency corresponds to the sliding rated value. Thus, in this case, only the screwdriver acting as the control unit is operated at the nominal value of £ f. At very high accuracy requirements, it is also possible to provide feedback to the screwdriver acting as a control unit by delaying the migration rate.

EN 200568 Β turn on the other screwdriver. The sliding rating is increased only when all slave screwdrivers have reached the current rating. It is noted, however, that the course of voltage increase is usually degressive, so that the initial voltage differences are compensated by the slower screwing process. The technically conceivable differences, in particular by their effect on the initial screw speed, can already be eliminated by determining the migration time value between the control and slave screw units as follows:

n tv = (0.05 ... 0.2) -fo where: - n - the vibration number of a single interval of screwing in the intervals;

- excitation frequency at the start of the interval.

In order to make the process more traceable, the nominal value, ie the target nominal value, should not be reached.

The invention will now be summarized once again with reference to the embodiment of Figure 4, some of which have the basic circuit shown in Figure 3. Here, the starting point is to use compact vibration transducer units (see Figures 1 and 2) and piezo-mechanical drives 24. Furthermore, a simple stepped nominal value was selected, which is the first to signal the chosen joint effort. To this end, all devices are connected via signal lines 27 to a unit 23 which provides a set value.

The lowest excitation frequency of the alternator 21 can be selected so that it is directly below the self-frequency of the screw spindle. The piezo-electric element 19, which is supported on the flange 6 and the end of the tube key housing 9, is excited through the power supply and signal transmission line. (Figures 1 and 2). The vibrations are transmitted to the screw 1 via the nut 4 and the vibration transducer 14 and subjected to vibration. Simultaneously, the piezo-mechanical drive 24 is actuated via the feed line 28. The difference generating unit 22 receives the excitation frequency measurement signal from the signal line 25 and compares it to the self-frequency signal of the screw spindle 1 via the signal line 25. A time member not shown here interrupts the operation of the alternator 2l for a short time. The self-frequency excited screw spindle 1 transmits its vibrations directly or indirectly to the piezo-electric element 2 or 19, which then provides a measurement signal. If the self-frequency is different from the excitation frequency, feedback is provided through the signal line 26 and the excitation frequency is approximated to the self-frequency to maintain resonance. This is done until the target data stored in the 23 units giving the setpoint value, in this case the desired biasing signal, is reached. Also, in the differential unit 22, it is checked that the self-frequency has changed from one measurement range to another. If this has not been done, no screwing can be performed since the excitation frequency is not sufficient to de-energize the screw spindle 1 sufficiently. Here, the feedback via the signal line 26 will work to increase the excitation energy.

It should be noted that each of these interruptions to the screwing process for measurement or re-balancing purposes is only a fraction of a second.

Once the rated value has been reached by all units, which nominal value corresponds to the selected prestress, the 23 units giving the rated value will automatically switch to the target nominal value. With this simple method, a very smooth screwing process can be achieved where all screw connections are equally loaded at the same time.

The main advantage of the process according to the invention is that it can be used for screw joints of various sizes and prestresses, while being energy efficient and precisely controllable and controllable.

An important advantage of the device according to the invention is that it can be used many times, is capable of simultaneously tightening or loosening a large number of screw joints, has a compact and robust construction and is easy and safe to handle. A further advantage is that the device according to the invention operates in a frequency range that is not audible and noticeable to the operator, thus eliminating the adverse health effects.

Claims (9)

PATENT CLAIMS A method for tightening or loosening screw connections using vibration energy, wherein the screw spindle or nut is preferably rotated by motor, characterized in that the screw spindle is excited by longitudinal vibrations, the self-frequency is measured and the excitation frequency is adjusted according to varying self-frequency during screwing. in order to keep the screw spindle in resonance at all times, and to control the excitation energy during the maximum stretching or contraction phase, the screw spindle in vibration is controlled to relieve stress or tension. Method according to claim 1, characterized in that the tail frequency is screw7 -611 HU 200568 Β treat the spindle as a standard value and compare it with the nominal value of the limit value of the screw spindle. When this is achieved, the excitation is interrupted and the screwing process 5 is completed. Method according to claim 1, characterized in that the piezoelectric motor for screwing is controlled by the same frequency as the self-frequency of the excitation or screw spindle. Method according to claim 1 or 2, characterized in that the method of stepwise tightening of at least two screw joints is stepped in, first by tightening to the first nominal value corresponding to the maximum prestress, and then after each screw connection. the first set point has been reached and continued until the last set point is applied continuously, with 20 additional stepped setpoints, if appropriate. Method according to claim 1 or 2, characterized in that the excitation energy is adapted to the screwing process so that it is continuously or intermittently increased as soon as the self-frequency of the screw spindle remains constant due to the stagnant screwing process, and continue until the nominal value is reached. Apparatus for tightening or loosening screw connections, preferably by means of a motor drive, and 35 units for directly or indirectly measuring the voltage of the screw spindle, characterized in that the screw spindle (1) is associated with a vibration transducer unit. 2; 19) is formed and supported, and the piezo-electric element 40 is connected to an alternator (21), which is connected to a differential generator (22), which is connected to the vibration sensor (12; 13) with a generator (21, also connected Apparatus according to claim 6, characterized in that the vibration transducer detection unit is formed as a piezo-electric element (2; 19) in the form of an annular disk. Device according to Claim 6 or 7, characterized in that the piezoelectric element (2; 19) is arranged between the screw head (15) or the nut (4) and the flange (6) to be fixed, and a power supply and signal line (3). 55 Apparatus according to claim 6 or 7, characterized in that the piezoelectric element (19) is disposed between the vibration transmitter (14) and the pipe wrench housing (9).